strange problem with asus mobo

Hi,
I have an ASUS-P5RD1-V mobo that I purchased in March. I assembled all the components and installed 256 mb of memory. It has windows-xp-sp2. It was working fine until recently. I installed another 256 mb of ram (same type and speed). Still working fine until recently when at startup, the machine would get stuck at mobo logo and would not go any further. I turn machine off and then back on, it works ok. sometimes i have to do this 2 or 3 times. and when it keeps going, at P.O.S.T., sometimes it says: overclocking failed, press f1 to go to setup. press f2 to continue with defaults. after f2, it loads windows and all is well. sometimes, the mobo log is distorted and fuzzy, sometimes it's ok. i also got a msg once: cmos check sum bad.

I have tried the memory sticks indivitually they seem to be ok. i even installed a single 512 mb new chip, same problem. I have tested cmos battery and it shows 3.2 volts.

rik,
thanks for your response. i tried to clear cmos. i moved the jumper to clear position. removed the battery. left it out for about 20 minutes. move the jumper to normal position. installed the battery. powered up. same problem. i updated the bios from the latest version (ami bios) from asus's website, still no joy.
it seems that the machine is getting stuck on asus logo on P.O.S.T. if i turn it off and on a few times, it keeps going.
i also noticed that it shows 65 mb less ram than i have installed. in the P.O.S.T. screen, it says 448 mb ram with 64 mb shared ram. where is this shared ram going?
one question: if the cpu goes bad, would it even boot to windows? would it even post?
if the mobo is bad, would it boot to windows? or not?
i'm just stumped on this one. i don't know if i sould scrap this mobo, and get another one to fit the cpu and my ram. but, i don't know if cpu is ok or not.
in any case we're talking about a few hundred dollars.
any suggestions?

i have 2 sticks of 256 mb
and 1 stick of 512 mb
they are all Kingston PC3200 DDR 400MHz
the 256 sticks are installed in bank 1 and 3 (blue) as the manual says.
the 512 stick is installed in bank 2 (black) as the manual says.
i know that the sticks have to match if there's more than 1.
but this mobo worked with just a single 256 mb ram installed in bank 1 before with no problem.

problem solved.
it was the power supply. using asus probe (mobo monitor), i noticed that the voltages put out by the psu is less than the required voltages. the 12 volt output was ok. the 5 volt output, was doing only 4.72. the 3.3 volts was doing only 3.13, and the 1.5 volt was doing only 1.22. as soon as i put the new psu, the pc booted right up with no problem at all. i repeated it several times to make sure, and every time, it had a clean boot.
thanks guys.